Abstract
Accessory splenosis (AS) is an uncommon condition that is formed from the lateral dorsal mesogastrium due to the defective union of separate splenic masses. It is often found next to the pancreatic tail and the hilum part of the spleen. The retroperitoneal is described as an unusual and uncommon site. We present a case of a 39-year-old woman with an AS who came to the clinic with a right abdominopelvic mass. Computerized tomography (CT) scan revealed a right retroperitoneal abdominal mass. Diagnostic laparoscopy and resection of the retroperitoneal mass were done, and histological investigation showed that the removed mass was a spleen. Although retroperitoneal abdominal AS is an unusual condition, it should be considered in the list of abdominopelvic mass differential diagnoses.